The sealing assemblies intended to equip the rolling bearings of wheel-hub units on the so-called “outer” or “outboard” flange side which supports the wheel, such as those described in U.S. Pat. No. 8,303,190 and in US2012/0177315, are formed by so-called “box” seals including a first and second annular screen, which have a generally L-shaped radial section and are mounted facing each other so as to define between the screens an annular chamber inside which a series of sealing lips are arranged, these being mounted on a fixed annular seal integral with one of the screens, generally the screen intended to remain stationary during use.
It has been found, however, that the screen, which is mounted on the ring rotating during use and therefore arranged adjacent to the wheel support flange, is displaced axially during use with respect to the bearing ring on which it is mounted, owing to the deflection of the flange, i.e. the deformations produced on the flange by the wheel when the vehicle goes around bends; therefore, it is known to provide the seat 20 for mounting the screen on the ring rotating during use with an axial stop, arranged axially on the opposite side to the flange, so as to axially lock in position on this side also the screen once it has been mounted in the mounting seat 20. The axial stop must, however, necessarily project axially with respect to the mounting seat 20 and, equally necessarily, the screen must have mounting dimensions which are the same as the dimensions of the mounting seat 20, namely smaller than the radial outer dimensions of the axial stop. Therefore, during mounting, the screen must manage to pass beyond the axial stop in the axial direction before being positioned inside the mounting seat 20 and it has been found that, in some cases, this passing movement tends to plastically deform the screen subsequently causing the engaging connection between screen and mounting seat 20 to come loose with the further drawback that the screen tends to rotate relative to the mounting seat 20 and about its own axis owing to the deformations.
These drawbacks, on the one hand, increase the friction acting on the sealing assembly, since the sealing lips not making sliding contact (and therefore not producing friction) may make sliding contact (and therefore produce friction) and the sealing lips which may be of the sliding contact type increase their interference and therefore the friction produced. Furthermore, in the case of relatively large displacements or rotations, an interference may be generated between the rotating screen and the stationary ring of the bearing, with the generation of very high friction levels and possible damage to the sealing assembly and even, in the worst case scenario, damage to the rolling members of the bearing.